Photoshop CC: Photomerge returns error message

I have updated to Photoshop CC from PS6. When I now try to use Photomerge, I get an error message - Error 1: Unable to create window - server interface error 'No component returned from create widget Line 388 >var w = new Window(res):

That usually means that you are missing some of the support files (like a failed installer, or restoring only part of the files from backup), or have mixed old and new versions of the photomerge scripts.